Palladium(II) complexes of phosphane ligands with ammonium-functionalized carbosilane substituents

Article abstract of DOI:10.1016/j.jorganchem.2008.03.015

The synthesis of diphenylarylphosphane and 1,2-bis(diarylphosphanyl)ethane ligands, where the aryl group is -C₆H₄CH₂CH₂SiMe₂CH₂OC₆H₄-3-NMe₂, their palladium

Full text of DOI:10.1016/j.jorganchem.2008.03.015

Journal of Organometallic Chemistry 693 (2008) 2147–2152
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Palladium(II) complexes of phosphane ligands with ammonium-functionalized
carbosilane substituents
*
*
Iván Dorado, Román Andrés, Ernesto de Jesús , Juan Carlos Flores
´
Departamento de Quımica Inorgánica, Universidad de Alcalá, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of diphenylarylphosphane and 1,2-bis(diarylphosphanyl)ethane ligands, where the aryl
group is –C6H4CH2CH2SiMe2CH2OC6H4-3-NMe2, their palladium(II) complexes, and their corresponding
ammonium-quaternized derivatives is described. These new phosphanes were devised as models of
potentially water-soluble dendritic carbosilane ligands, although the solubility brought about by the
quaternized N-trimethylanilinium groups is scarce. The palladium(II) complexes have been fully charac-
terized by 1H, 13C, and 31P NMR spectroscopy and mass spectrometry, and have been tested in the Hiyama
cross-coupling reaction between tri(methoxy)phenylsilane and 3-bromopyridine in aqueous sodium
hydroxide solution.
Received 11 February 2008
Received in revised form 11 March 2008
Accepted 12 March 2008
Available online 18 March 2008
Keywords:
Palladium
Phosphane Ligands
Dendrimers
Ó 2008 Elsevier B.V. All rights reserved.
Aqueous-phase catalysis
C–C coupling
1. Introduction
minal groups [7–9]. One possible approach to render a phosphane
ligand water-soluble is to functionalize the focal point and periph-
The synthesis and study of ligands and metal complexes for
aqueous-phase homogeneous catalysis is currently an active area
in organometallic chemistry [1]. Aryl and alkyl tertiary phosphanes
are amongst the most common ligands present in transition-metal
catalysis, but they are hydrophobic and lack water solubility.
Hydrophilicity can be introduced into a phosphane by attaching
nonionic groups, for instance hydroxyalkyl or polyether substitu-
ents, although water solubility is usually achieved by making use
of anionic or cationic functions, such as sulfonate or ammonium
groups [2]. We have been involved in the modification of early
and late transition-metal catalysts with carbosilane dendrimers
and dendrons [3,4]. These macromolecules can serve as solubiliz-
ers of hosted catalysts [5] as their interaction with the solvent de-
pends mainly on the type of end-groups they contain. In this
direction, we recently reported, in collaboration with Galindo
and co-workers, the first example of a metal complex that is solu-
ble in supercritical CO2 as it contains trialkylsilyl-terminated den-
drons that are linked through their focal point to the phenyl groups
of a triphenylphosphane ligand [6].
ery of a carbosilane dendron with the chosen phosphane and
hydrophilic groups, respectively. Unlike conventional water-solu-
ble complexes, the metal centre in these dendritic complexes
would be surrounded by a relatively hydrophobic block consti-
tuted by the carbosilane branches. One possible advantage of such
systems could be their double role of water-soluble organometallic
catalysts and phase-transfer catalysts. At the water-organic phase
interface, the dendrons might change their conformation exposing
their hydrophobic interior to the organic solvent and allowing the
organic substrates to diffuse into the dendrimer interior where the
catalyst is located [10].
Several methods have been reported for the focal-point func-
tionalization of carbosilane dendrons with phosphorus-donor
ligands [11–13]. 4-Bromostyrene is a suitable starting point be-
cause the carbosilane dendrimer can be grown divergently from
the vinyl group by the usual iterative hydrosilylation/allylation
reaction sequence. The resulting bromoarene can then be lithiated
and finally treated with the appropriate chlorophosphane [11]. For
our goal, however, these two processes must be compatible with
the incorporation of hydrophilic groups. Herein, we describe an
appropriate pathway for the preparation of mono- and bidentate
phosphanes functionalized with ammonium groups that are mod-
els for carbosilane dendrimers (zeroth-generation dendrimers).
Their palladium(II) complexes are also prepared and tested in a
Hiyama cross-coupling reaction.
Spherical carbosilane dendrimers have already been rendered
water-soluble by the incorporation of sulfonate or ammonium ter-
* Corresponding authors. Tel.: +34 91 885 4603; fax: +34 91 885 4683.
E-mail addresses: ernesto.dejesus@uah.es (E. de Jesús), juanc.flores@uah.es (J.C.
Flores).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.03.015

2148
I. Dorado et al. / Journal of Organometallic Chemistry 693 (2008) 2147–2152
4:4:1 ratio. These resonances were respectively assigned to the ex-
2. Results and discussion
pected dichlorido [PdCl2(4)], chloridobromido [PdClBr(4)], and dib-
romido [PdBr2(4)] complexes after an analysis of the position and
isotopic distribution of peaks appearing in the ESI + MS spectrum
of the crude reaction mixture. Several experiments were per-
formed to corroborate the existence of halide exchange between
palladium dichloride and a bromide salt contaminating the phos-
phane ligand. Thus, the 31P{1H} NMR spectrum of the product con-
tains almost exclusively the 31P resonance assigned to the
dichlorido complex when the sample of 4 used for the reaction
was previously isolated and purified (see Section 4), the dibromid-
opalladium complex was the only product detected when an ex-
cess of lithium bromide was added to the reaction mixture, and,
finally, a solution of the dibromido derivative in [D6]acetone
turned from yellow to intense red after addition of sodium iodide
due to the formation of the diiodido complex (dP = 63.6 ppm).
The most likely source of bromide is lithium bromide, which could
be already present in the commercial solution of tert-butyllithium
or could be originated as a by-product in the lithiation of bromoa-
rene 2 [16]. Treatment of the non-isolated monophosphane 3 with
[PdCl2(COD)] also afforded a mixture of dichlorido (dP = 23.8 ppm),
bromidochlorido (dP = 23.5 ppm), and dibromido (dP = 21.4 ppm)
complexes, all as trans diastereoisomers.
The dibromido complexes 5 and 6 were obtained on a prepara-
tive scale by addition of an excess of LiBr to the reaction media
(Scheme 2) and were isolated after workup as spectroscopically
and analytically pure yellow solids. The dimethylamine groups of
these complexes were quaternized by treatment with an excess
of iodomethane at 65 °C in thf to give complexes 7 and 8, respec-
tively. A bromido/iodido ligand exchange was also observed at
the metal centers in 7 and 8 (MS and 31P NMR evidence) whereby
the iodide ions originating from quaternization of the amine appar-
ently exchange their positions with the bromido ligands bound to
palladium. However, elemental analysis of the isolated solids indi-
cated that the halido ligands and halide counterions were both io-
dine. The most likely explanation for this is that the bromido/
iodido ligand exchange is followed by a Finkelstein substitution
[17] in which the bromide anions react with the excess of iodo-
methane to give bromomethane [18,19]. Compounds 7 and 8 were
obtained as red solids that are fairly insoluble in most common or-
ganic solvents, therefore their NMR characterization was per-
formed in [D6]DMSO. Although they are soluble in the aqueous
catalytic medium at the temperature and under the conditions de-
scribed below, they were found to be insoluble in water at room
temperature.
The palladium complexes 5–8 were fully characterized by ele-
mental analysis, 1H, 13C, and 31P NMR spectroscopy, and mass spec-
trometry. The ESI+ mass spectra show the molecular peaks with the
expected isotopic distributions for the neutral complexes 5 and 6,
and the molecular peaks after the loss of one or more iodide anions
for 7 and 8. Mass spectra and elemental analyses served to confirm
the replacement of bromide by iodide in the quaternized com-
plexes. The 31P NMR chemical shifts of the bidentate ligands in
the dibromido (6) and diiodido (8) complexes (dP = 65.3 and
66.3 ppm, respectively) are similar to those reported for their 1,2-
bis(diphenylphosphanyl)ethane analogues [PdX2(dppe)] (dP = 64.4
and 66.7 ppm for X = Br [20] and I [21], respectively). According
to the NMR spectroscopic data, the two monophosphane complexes
are obtained as a unique isomer but with opposite stereochemistry
(trans for neutral 5 and cis for dicationic 7). For instance, the 31P
chemical shift of 5 (dP = 21.4 ppm) is very similar to that observed
for the trans PPh3 analogue (dP = 22.1 ppm) [22] and to that ex-
pected from the empirical correlation reported between the chem-
ical shifts of free and coordinated phosphines (dP ꢁ 23 and 35 ppm
for trans and cis, respectively) [23]. Moreover, the 13C resonance of
the ipso phenyl carbon (dC = 131.4 ppm) appears as a pseudo triplet
2.1. Synthesis of phosphane ligands and complexes
The amino-functionalized aryl bromide ArBr (2; Ar = C6H4-
CH2CH2SiMe2CH2OC6H4-3-NMe2) was obtained by the sequence of
reactions depicted in Scheme 1. The first step consists of the vinyl-
hydrosilylation of 4-bromostyrene with (chloromethyl)dimethylsi-
lane in toluene at room temperature in the presence of Speier’s
platinum catalyst (hydrogen hexachloroplatinate). This hydrosily-
lation reaction affords exclusively the anti-Markovnikov product 1
under these conditions and was monitored by 1H NMR spectroscopy
up to completion. Subsequent nucleophilic substitution of the
terminal chloride in 1 by the phenolate group of 3-dimethylamino-
phenol was carried out in dmf at 80 °C with an excess of K2CO3 as
base. These conditions are based on those reported by Astruc and
co-workers [14] with the only difference that addition of NaI as a
catalyst was omitted in our case. The reaction was followed by mon-
itoring the shift of the 1H NMR resonance of the SiCH2X methylene
from d = 2.76 ppm in 1 to d = 3.56 ppm in 2.
The monophosphane PPh2Ar (3) and the diphosphane
Ar2PCH2CH2PAr2 (4) were synthesized by treatment of LiAr, which
was obtained in situ, with the corresponding chlorophosphane at
ꢀ78 °C (Scheme 2). The use of tert- instead of n-butyllithium for
the lithiation of bromoarene 2 was found to be essential as the less
nucleophilic nBuLi produces important quantities of the homocou-
pled biaryl (Ar–Ar) product, which was identified by mass spec-
trometry. The new phosphane ligands were isolated as described
in Section 4 and characterized spectroscopically. The chemical shifts
of their 31P resonances (d = ꢀ5.0 ppm for 3 and d = ꢀ13.0 ppm for 4)
are very similar to those found in PPh3 (d = ꢀ4.2 ppm) and
PPh2CH2CH2PPh2 (d = ꢀ12.1) [15]. In addition, the ethylene bridge
protons of 4 give a broad resonance at d = 2.05 ppm in the 1H NMR
spectrum due to coupling with the two magnetically nonequivalent
phosphorus nuclei, as in the parent 1,2-bis(diphenylphospha-
nyl)ethane. Both dimethylamine-functionalized phosphanes were
obtained as colorless oils that readily oxidize in the presence of
traces of air. They were therefore prepared and used in situ in sub-
sequent reactions.
Palladium complexes of monodentate 3 and bidentate phos-
phane 4 were obtained by displacement of the labile 1,5-cycloocta-
diene (COD) ligand from [PdCl2(COD)] with the corresponding
phosphane in thf. However, the residues obtained after elimination
of volatiles were found to contain a mixture of three different com-
plexes. For instance, the 31P{1H} NMR spectrum of the residue ob-
tained from the reaction with diphosphane 4 contains a singlet at
d = 64.1 ppm, a set of two doublets at d = 64.2 and 64.8 ppm
(JP,P = 13.1 Hz), and a singlet at d = 65.3 ppm in approximately a
NMe2
Cl
O
NMe2
SiMe2
SiMe2
HSiMe2CH2Cl
toluene, [Pt]
OH
K2CO3,
DMF, 80 °C
Br
Br
Br
1
2
Scheme 1.

I. Dorado et al. / Journal of Organometallic Chemistry 693 (2008) 2147–2152
2149
NMe3+I–
Me2
O
Si
Br
PPh2
Pd
PPh2
I
I
PPh2Cl
[PdCl2(COD)]
LiBr (excess)
MeI (excess)
65 °C
PPh2Ar
ArPh2P Pd PPh2Ar
THF,– 78 °C
3
Br
5
Me2Si
O
7
NMe3+I–
2 + tBuLi
NMe3+I–
NMe3+I–
O
O
SiMe2 Me2Si
Ar2
P
PAr2
P
Cl2PCH2CH2PCl2
THF, – 78 °C
MeI (excess)
65 °C
[PdCl2(COD)]
LiBr (excess)
PdI2
PdBr2
PAr2
P
P
Ar2
4
6
SiMe2 Me2Si
O
O
NMe3+I–
Ar =
O
SiMe2
NMe3+I–
NMe2
8
Scheme 2.
[1J(13C–31P) + 3J(13C–31P) = 50 Hz], as expected for trans palladium
phosphane complexes where the 2J(31P–31P) coupling constant is
of the order of a few hundred hertz [24]. The cis stereochemistry
of complex 7 is in agreement with the splitting of the aromatic
13C resonances coupled to 31P into doublets, as expected for the nor-
mal value of around 0 Hz for the 2J(31P–31P) coupling constant in cis
palladium complexes [24,25]. This cis arrangement of complex 7
(dP = 31.6 ppm), in spite of the cationic nature of the ligands, con-
trasts with the trans stereochemistry found in the neutral analogue
[PdI2(PPh2Ar)2] (dP = 12.3 ppm) [26] and in [PdI2(PPh3)2]
(dP = 13.3 ppm) [27].
We tried to increase the water solubility of the ionic compounds
by replacing the iodide with nitrate. In a test carried out in an NMR
tube, a suspension of 7 in D2O became solubilized into the aqueous
phase after treatment with two equivalents of AgNO3 for 1 h. The
1H NMR spectrum of the yellow solution obtained after filtration
showed the signals of a single species with a similar pattern of res-
onances to that of compound 7 [28]. However, all attempts to scale
the preparation up failed to give a pure product.
[33], amongst other organometallic reagents. Hiyama reactions in
water have recently been described by our group and others using
a variety of Pd precatalysts and, usually, organosiloxanes activated
with sodium or potassium hydroxide [34–38]. We chose the cou-
pling of tri(methoxy)phenylsilane and 3-bromopyridine, under
our previously reported conditions [36] (Scheme 3), to test the effi-
ciency of the palladium complexes 7 and 8 as aqueous-phase cat-
alysts. We also tested the neutral complexes
5 and 6 for
comparison. Table 1 summarizes our results. Conversions obtained
with the cationic precursors 7 and 8 were high (80–95%) but lower
than those obtained with the neutral precursors 5 and 6. We have
previously observed that [PdCl2(PPh3)2] and other precursors with-
out water-solubilizing groups afford nearly quantitative yields for
the same reaction under the same conditions but are more prone
to deactivate by precipitation of Pd black [36]. This role of the
water-solubilizing ligands might also lay behind the activities
shown by the aqueous solutions that were reused after extraction
of the organic compounds (Table 1), where the complete inactivity
2.2. Hiyama coupling in aqueous solution
Si(OMe)3
The palladium-catalyzed aryl–aryl cross-coupling reaction is a
simple, efficient, and versatile route to the formation of carbon–
carbon bonds that is commonly used in modern organic synthesis
[29,30] to give complex products in a one-step reaction between an
aryl halide and an organoborane (Suzuki reaction) [31], organost-
annane (Stille reaction) [32], or organosilane (Hiyama reaction)
Br
NaOH/H2O
+
1 mol % [Pd]
140 C, 2 h
N
N
°
Scheme 3.

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I. Dorado et al. / Journal of Organometallic Chemistry 693 (2008) 2147–2152
Table 1
bined pentane solutions were evaporated to dryness to give 1 as a
white oily solid (2.1 g, 94%). Anal. Calc. for C11H16BrClSi (291.69): C,
45.29; H, 5.53. Found: C, 45.72; H, 5.48%. 1H NMR (CDCl3,
200 MHz): d = 7.37 (d, JH,H = 8.5, 2H, C6H4), 7.06 (d, JH,H = 8.5,
2H, C6H4), 2.76 (s, 2H, CH2Cl), 2.61 (m, 2H, PhCH2), 0.98 (m, 2H,
CH2Si), 0.12 (s, 6H, SiMe2) ppm. 13C{1H} NMR (CDCl3, 75 MHz):
d = 143.3 (s, C6H4, C bonded to CH2), 131.3 (s, C6H4), 129.5 (s,
C6H4), 119.3 (s, C6H4, Cipso bonded to Br), 30.1 (s, CH2Cl), 29.2 (s,
PhCH2), 15.6 (s, CH2Si), ꢀ4.52 ppm (s, SiMe2).
Hiyama coupling of 3-bromopyridine and tri(methoxy)phenylsilane in aqueous
alkaline medium catalyzed by Pd complexes 5–8
Pd catalysta
Conv. (%)b
Conv. (2nd run) (%)c
3
3
5
6
7
8
100
100
95
0
0
5
1
80
a
1 mol% of Pd catalyst with respect to 3-bromopyridine, see Section 4 for details.
Conversions determined by 1H NMR spectroscopy.
Conversions obtained using the aqueous solution from the first run after
b
c
4.3. Synthesis of BrAr (2; Ar = C6H4-4-CH2CH2SiMe2CH2OC6H4-3-
NMe2)
extraction of the organic products and addition of further reagents.
A mixture of 1 (2.10 g, 7.20 mmol), 3-(dimethylamino)phenol
(1.02 g, 7.20 mmol), and K2CO3 (4.50 g, 32.6 mmol) in dmf
(25 mL) was stirred overnight at 80 °C. The solvent was then re-
moved under vacuum at 60 °C and the residue extracted with pen-
tane (2 ꢂ 25 mL). The combined pentane solutions were
evaporated to dryness to give 2 as a pale-brown solid (2.5 g,
88%). Anal. Calc. for C19H26BrNOSi (392.41): C, 58.16; H, 6.68; N,
3.57. Found: C, 58.15; H, 6.43; N, 4.13%. 1H NMR (CDCl3,
of the neutral complexes contrasts with the very poor but positive
activities shown by the cationic catalysts.
3. Conclusions
The phosphanes described in this work are models for the syn-
thesis of potentially water-soluble dendritic ligands, although the
solubility brought about by the hydrophilic N-trimethylanilinium
groups is poor at present. Nevertheless, enhancements are possible
by tuning the nature and multiplying the number of the hydro-
philic end-groups of the carbosilane dendrons during the construc-
tion of the phosphane ligands.
3
3
300 MHz): d = 7.35 (d, JH,H = 8.2, 2H, BrC6H4), 7.06 (d, JH,H = 8.2,
3
2H, BrC6H4), 7.12 (t, JH,H ꢁ 8.2, 1H, C6H4N), 6.31 (overlapped m,
3H, C6H4N), 3.56 (s, 2H, CH2O), 2.92 (s, 6H, NMe2), 2.65 (m, 2H,
PhCH2), 1.00 (m, 2H, CH2Si), 0.12 (s, 6H, SiMe2) ppm. 13C{1H}
NMR (CDCl3, 75 MHz): d = 162.5 (s, C6H4N, C bonded to O), 151.9
(s, C6H4N, C bonded to N), 143.8 (s, BrC6H4, C bonded to CH2),
131.2 (s, BrC6H4), 129.6 (s, BrC6H4), 129.5 (s, C6H4N), 119.1 (s,
BrC6H4, C bonded to Br), 105.5 (s, C6H4N), 101.9 (s, C6H4N), 99.2
(s, C6H4N), 59.6 (s, CH2O), 40.6 (s, NMe2), 29.2 (s, C6H4CH2), 15.7
(s, CH2Si), ꢀ4.76 ppm (s, SiMe2). MALDI-TOF MS: m/z 392.1
[M+H]+ (calcd. 392.1).
4. Experimental
4.1. Reagents and general techniques
All operations were performed under argon by using Schlenk or
dry box techniques. Solvents were dried and distilled under argon
(thf and diethyl ether from sodium benzophenone ketyl; hexane
and pentane from sodium/potassium alloy; CH2Cl2 from P2O5; ace-
tonitrile and CDCl3 from finely ground calcium hydride) [39]. Un-
less otherwise stated, reagents were obtained from commercial
sources and used as received. [PdCl2(COD)] (COD = 1,5-cyclooctadi-
ene) was prepared according to reported procedures [40]. 1H, 13C,
and 31P NMR spectra were recorded with Varian Gemini-200, Mer-
cury VX-300, or UnityPlus-500 spectrometers. Chemical shifts (d,
4.4. Synthesis of P(C6H5)2Ar (3)
A 1.7 M solution of tert-butyllithium in pentane (1.00 mL,
1.68 mmol) was added with a syringe to a solution of bromoarene
2 (0.659 g, 1.68 mmol) at ꢀ78 °C in thf (25 mL). Stirring was con-
tinued at the same temperature for 60 min, then PPh2Cl (0.31 mL,
1.7 mmol) was added and the reaction mixture was allowed to
slowly warm to room temperature overnight. The solvent was then
removed under vacuum and the residue extracted with toluene
(2 ꢂ 10 mL). Evaporation of the toluene solution to dryness yielded
3 as a spectroscopically pure colorless oil (0.79 g, 94%). 1H NMR
(CDCl3, 300 MHz): d = 7.34–7.10 (overlapped m, 15H, PC6H5,
PC6H4, and C6H4N), 6.35 (overlapped m, 3H, C6H4N), 3.60 (s, 2H,
CH2O), 2.94 (s, 6H, NMe2), 2.73 (m, 2H, C6H4CH2), 1.06 (m, 2H,
CH2Si), 0.15 (s, 6H, SiMe2) ppm. 13C{1H} NMR (C6D6, 75 MHz):
d = 163.2 (C6H4N, C bonded to O), 152.4 (s, C6H4N, C bonded to
N), 145.9 (s, PC6H4, C bonded to CH2), 138.4 (d, JC,P = 12, PC6H5,
ppm) are quoted relative to SiMe4 (1H, 13C) or 85% H3PO4 31P),
(
and were measured by internal referencing to the deuterated sol-
vent (13C and residual 1H resonances), or by the substitution meth-
od (31P). Coupling constants (J) are given in Hz. The coupling
constants of pseudo triplets in the 13C NMR spectra (see results
and discussion) correspond to J(13C–31PA) + J(13C–31PA ). Samples
0
for MALDI-TOF mass spectrometry were prepared in a 1,8,9-tri-
hydroxyanthracene (dithranol) matrix and spectra were recorded
with a Bruker Reflex II spectrometer equipped with a nitrogen laser
emitting at 337 nm and operated in the reflection mode at an
accelerating voltage in the range 23–25 kV. The Analytical Services
of the Universidad de Alcalá recorded the ESI mass spectra in
methanol with a Thermoquest–Finnigan Automass Multi spec-
trometer. The C, H, and N analyses were performed in duplicate
by the above services with a LECO CHNS-932 microanalyzer.
C
C
ipso), 134.5 (d, JC,P = 20, PC6H4, Cortho), 134.1 (d, JC,P = 20, PC6H5,
ortho), 129.9 (s, C6H4N), 128.7 (d, JC,P = 20, PC6H5, Cpara), 128.6 (d,
JC,P = 7, PC6H5, Cmeta), 128.5 (d, JC,P = 7, PC6H4, Cmeta), 102.2 (s,
C6H4N), 106.2 (s, C6H4N), 100.0 (s, C6H4N), 59.7 (s, CH2O), 40.3 (s,
NMe2), 29.9 (s, C6H4CH2), 15.8 (s, CH2Si), ꢀ4.73 ppm (s, SiMe2); C
bonded to
P
in PC6H4 not observed. 31P{1H} NMR (C6D6,
202 MHz): d = ꢀ5.0 ppm.
4.2. Synthesis of 4-BrC6H4CH2CH2SiMe2CH2Cl (1)
4.5. Synthesis of Ar2PCH2CH2PAr2 (4)
An excess of (chloromethyl)dimethylsilane (1.5 mL, 12.3 mmol)
was added dropwise to a solution of 4-bromostyrene (1.40 g,
7.65 mmol) at 0 °C in toluene (25 mL) containing hydrogen hexa-
chloroplatinate (5 drops of a 2 ꢂ 10ꢀ3 M solution in 2-propanol)
as hydrosilylation catalyst and this mixture was stirred overnight
at room temperature. The solvent was then removed under vac-
uum and the residue extracted with pentane (2 ꢂ 15 mL). The com-
A 1.7 M solution of tert-butyllithium in pentane (0.77 mL,
1.3 mmol) was added with a syringe to a solution of bromoarene
2 (0.51 g, 1.30 mmol) at ꢀ78 °C in thf (25 mL). This mixture was
stirred at the same temperature for 60 min and then
Cl2PCH2CH2PCl2 (48 lL, 0.32 mmol) was added with a syringe.
The reaction mixture was allowed to warm slowly to room temper-

I. Dorado et al. / Journal of Organometallic Chemistry 693 (2008) 2147–2152
2151
ature overnight, then the solvent was removed under vacuum and
the residue extracted with toluene (2 ꢂ 10 mL). Evaporation of the
toluene solution to dryness gave 4 as a spectroscopically pure col-
orless oil (0.36 g, 84%). 1H NMR (CDCl3, 300 MHz): d = 7.23 (m, 8H,
PC6H4, Hortho), 7.10 (overlapped m, 12H, PC6H4 and C6H4N), 6.34
(overlapped m, 12H, C6H4N), 3.59 (s, 8H, CH2O), 2.93 (s, 24H,
NMe2), 2.69 (m, 8H, C6H4CH2), 2.05 (br. pseudo t, 4 H, PCH2), 1.03
(m, 8H, CH2Si), 0.13 (s, 24H, SiMe2) ppm. 13C{1H} NMR (CDCl3,
75 MHz): d = 162.6 (s, C6H4N, C bonded to O), 152.0 (s, C6H4N, C
bonded to N), 145.4 (s, PC6H4, C bonded to CH2), 135.1 (d,
JC,P = 12, PC6H4, C bonded to P), 132.8 (pseudo t, JC,P = 20, PC6H4,
2.90 (s, 24H, NMe2), 2.80 (m, 8H, C6H4CH2), 2.44 (m, 4H, PCH2CH2P),
1.09 (m, 8H, CH2Si), 0.15 (s, 24H, SiMe2). 1H NMR (CDCl3,
3
3
300 MHz): d = 7.69 (dd, JH,P = 11.6, JH,H = 8.2, 8H, PC6H4, Hortho),
3
3
7.28 (d, JH,H = 8.2, 8H, PC6H4, Hmeta), 7.08 (t, JH,H = 8.4, 4H,
C6H4N), 6.37 (br., 12H, C6H4N), 3.58 (s, 8H, CH2O), 2.93 (s, 24H,
NMe2), 2.74 (m, 8H, C6H4CH2), 2.22 (br., 4H, PCH2CH2P), 1.04 (m,
8H, CH2Si), 0.14 (s, 24H, SiMe2) ppm. 13C{1H} NMR ([D6]acetone,
75 MHz): d = 163.5 (s, C6H4N, C bonded to O), 152.2 (s, C6H4N, C
bonded to N), 150.1 (s, PC6H4, C bonded to CH2), 134.7 (pseudo t,
JC,P = 12, PC6H4, Cortho), 130.4 (s, C6H4N), 129.1 (pseudo t, JC,P = 12,
PC6H4, Cmeta), 127.2 (dd, JC,P = 59 and 4, PC6H4, C bonded to P),
106.7 (s, C6H4N), 103.8 (s, C6H4N), 100.5 (s, C6H4N), 60.3 (s,
CH2O), 41.2 (s, NMe2), 16.1 (s, CH2Si), ꢀ4.61 ppm (s, SiMe2); the
C6H4CH2 resonance is obscured by the solvent and PCH2CH2P was
not found. 31P{1H} NMR ([D6]acetone, 202 MHz): d = 65.3 ppm.
MALDI-TOF MS: m/z 1602.5 [M]+ (calcd. 1602.4), 1523.5 [MꢀBr]+
(calcd. 1523.5), 1444.6 [Mꢀ2Br]+ (calcd. 1444.6).
Cortho), 129.6 (s, C6H4N), 127.9 (pseudo t, JC,P = 7, PC6H4, Cmeta),
105.5 (s, C6H4N), 101.9 (s, C6H4N), 99.2 (s, C6H4N), 59.8 (s, CH2O),
40.7 (s, NMe2), 29.6 (s, C6H4CH2), 24.1 (br. s, CH2CH2), 15.6 (s,
CH2Si), ꢀ4.72 (s, SiMe2) ppm. 31P{1H} NMR (CDCl3, 202 MHz):
d = ꢀ13.0 ppm.
4.6. Synthesis of [PdBr2{P(C6H5)2Ar}2] (5)
4.8. Synthesis of [PdI2{P(C6H5)2Ar+}2][I]2 (7; Ar+ = C6H4-4-
+
A thf solution (25 mL) of phosphane 3 was prepared according to
the procedure described above from tert-butyllithium (0.88 mL,
1.5 mmol, 1.7 M in pentane), bromoarene 2 (0.585 g, 1.49 mmol),
and PPh2Cl (0.27 mL, 1.41 mmol). Once the reaction mixture had
reached room temperature (16 h) a solution of [PdCl2(COD)]
(0.200 g, 0.70 mmol) in thf (20 mL) and a large excess of LiBr
(0.2 g) were added and stirring was maintained overnight at room
temperature. The solvent was then removed under vacuum and
the residue extracted with CH2Cl2 (2 ꢂ 10 mL). After evaporation
of the solvent, the residue was washed with pentane (2 ꢂ 15 mL)
and dried in vacuo to yield 5 as a yellow solid (0.73 g, 83%). Anal.
Calc. for C62H72Br2N2O2P2PdSi2 (1261.6): C, 59.03; H, 5.75; N, 2.22.
Found: C, 59.08; H, 5.75; N, 2.06%. 1H NMR (CDCl3, 300 MHz):
CH2CH2SiMe2CH2OC6H4-3- NMe3
)
Methyl iodide (0.20 mL, 3.21 mmol) was added with a syringe
to a solution of 5 (0.600 g, 0.476 mmol) in thf (25 mL). The reaction
mixture was stirred at 65 °C for 16 h and the solvent then removed
under vacuum. The residue thus obtained was washed with diethyl
ether (2 ꢂ 15 mL) and dried in vacuo to yield 7 as a red solid
(0.74 g, 95%). Anal. Calc. for C64H78I4N2O2P2PdSi2 (1639.5): C,
46.89; H, 4.80; N, 1.71. Found: C, 45.76; H, 4.41; N, 1.74%. 1H
NMR ([D6]DMSO, 300 MHz): d = 7.75–7.19 (overlapped m, 36H,
C6H5 and C6H4), 3.73, (s, 4H, CH2O), 3.56 (s, 18H, NMe3I), 2.74 (m,
4H, C6H4CH2), 1.03 (m, 4H, CH2Si), 0.12 (s, 12H, SiMe2) ppm.
13C{1H} NMR ([D6]DMSO, 75 MHz): d = 161.3 (s, C6H4N, C bonded
to O), 148.3 (s, C6H4N, C bonded to N), 147.7 (s, PC6H4, Cipso bonded
to CH2), 134.5 (d, JC,P = 10, PC6H4, Cortho), 133.8 (d, JC,P = 10, PC6H5,
d = 7.65 (overlapped m, 12H, PC6H5), 7.35 (overlapped m, 12H,
3
PC6H5 and PC6H4), 7.20 (d, JH,H = 7.9,
4 H, PC6H4), 7.11 (t,
3JH,H = 8.0, 2H, C6H4N), 6.33 (overlapped m, 6H, C6H4N), 3.58 (s, 4H,
CH2O), 2.91 (s, 12H, NMe2), 2.71 (m, 4H, C6H4CH2), 1.03 (m, 4H,
CH2Si), 0.12 (s, 12H, SiMe2) ppm. 13C{1H} NMR (CDCl3, 75 MHz):
d = 162.6 (s, C6H4N, C bonded to O), 152.0 (s, C6H4N, C bonded to
N), 147.7 (s, PC6H4, C bonded to CH2), 135.4 (pseudo t, JC,P = 13,
PC6H4, Cortho), 134.9 (pseudo t, JC,P = 12, PC6H5, Cortho), 131.4 (pseudo
t, JC,P = 50, PC6H5, Cipso), 130.3 (br. s, PC6H5, Cpara), 129.6 (s, C6H4N),
127.7 (pseudo t, JC,P = 10, PC6H5, Cmeta), 127.5 (pseudo t, JC,P = 10,
PC6H4, Cmeta), 105.5 (s, C6H4N), 101.8 (s, C6H4N), 99.3 (s, C6H4N),
59.7 (s, CH2O), 40.7 (s, NMe2), 29.7 (s, C6H4CH2), 133.3 (br, s,
PC6H4, Cortho), 133.0 (s, C6H4N), 15.4 (s, CH2Si), ꢀ4.74 ppm (s, SiMe2);
Cipso of PC6H4 was not found. 31P{1H} NMR (CDCl3, 202 MHz):
d = 21.4 ppm. ESI+MS: m/z 1260.0 [M+H]+ (calcd. 1259.2).
Cortho), 130.9 (s, C6H4N), 130.8 (s, PC6H5, Cpara), 128.3 (d, JC,P = 12,
PC6H5, Cmeta), 127.6 (d, JC,P = 12, PC6H4, Cmeta), 114.6 (s, C6H4N),
111.3 (s, C6H4N), 106.9 (s, C6H4N), 60.3 (s, CH2O), 55.8 (s, NMe3I),
28.5 (s, C6H4CH2), 14.3 (s, CH2Si), ꢀ5.29 ppm (s, SiMe2); Cipso of
PC6H4 and PC6H4 were not found. 31P{1H} NMR ([D6]DMSO,
202 MHz): d = 31.4 ppm. ESI+MS: m/z 1510.5 [MꢀI]+ (calcd.
1511.1), 691.7 [Mꢀ2I]2+ (calcd. 692.1).
4.9. Synthesis of [PdI2(Ar+2PCH2CH2 PAr+2)2][I]4 (8)
Methyl iodide (0.10 mL, 1.61 mmol) was added with a syringe
to a solution of 6 (0.30 g, 0.187 mmol) in thf (25 mL) and the reac-
tion mixture was stirred at 65 °C for 16 h. The solvent was then re-
moved under vacuum and the residue washed with diethyl ether
(2 ꢂ 15 mL) and dried in vacuo to yield 8 as a red solid (0.41 g,
96%). Anal. Calc. for C82H120I6N4O4P2PdSi4 (2268.0): C, 43.43; H,
5.33; N, 2.47. Found: C, 43.61; H, 5.38; N, 2.51%. 1H NMR
4.7. Synthesis of [PdBr2(Ar2PCH2CH2PAr2)] (6)
Chelate ligand 4 was prepared in thf (25 mL), as described
above, from tert-butyllithium (0.90 mL, 1.53 mmol, 1.7 M solution
in pentane), bromoarene 2 (0.600 g, 1.53 mmol), and Cl2PCH2-
CH2PCl2 (58 lL, 0.382 mmol). The reaction mixture was allowed
to warm slowly to room temperature for 16 h before the addition
of a solution of [PdCl2(COD)] (0.110 g, 0.385 mmol) in thf (20 mL)
and a large excess of LiBr (0.2 g). This mixture was stirred over-
night at room temperature, then the solvent was removed under
vacuum and the residue extracted with CH2Cl2 (2 ꢂ 10 mL). After
evaporation of the solvent, the residue was washed with pentane
(2 ꢂ 15 mL) and dried in vacuo to yield 6 as a yellow solid
(0.50 g, 81%). Anal. Calc. for C78H108Br2N4O4P2PdSi4 (1606.3): C,
58.33; H, 6.78; N, 3.49. Found: C, 57.61; H, 6.87; N, 3.03%. 1H
3
3
([D6]DMSO, 300 MHz): d = 7.67 (br. t, JH,P ꢁ JH,H ꢁ 10, 8H, PC6H4,
3
H
ortho), 7.50 (overlapped m, 12H, C6H4N), 7.41 (d, JH,H = 7.3, 8H,
3
PC6H4, Hmeta), 7.20 (d, JH,H = 7.3, 4H, C6H4N), 3.79 (s, 8H, CH2O),
3.59 (s, 36H, NMe3I), 2.75 (m, 8H, C6H4CH2), 2.39 (br., 4H,
PCH2CH2P), 1.04 (m, 8H, CH2Si), 0.13 (s, 24H, SiMe2) ppm. 13C{1H}
NMR ([D6]DMSO, 75 MHz): d = 161.4 (s, C6H4N, C bonded to O),
148.3 (s, C6H4N, C bonded to N), 147.8 (s, PC6H4, C bonded to
CH2), 130.3 (s, C6H4N), 133.3 (br. s, PC6H4, Cortho), 127.6 (br. s,
PC6H4, Cmeta), 126.1 (d, JC,P = 54, PC6H4, C bonded to P), 114.7 (s,
C6H4N), 111.4 (s, C6H4N), 106.8 (s, C6H4N), 60.4 (s, CH2O), 55.9 (s,
NMe3I), 28.5 (s, C6H4CH2), 14.2 (CH2Si), ꢀ5.2 ppm (s, SiMe2);
PCH2CH2P was not found. 31P{1H} NMR ([D6]DMSO, 202 MHz):
d = 66.3 ppm. ESI+ MS: m/z 628.45 [Mꢀ3I]3+ (calcd. 628.47),
581.14 [Mꢀ4IꢀCH3]3+ (calcd. 581.16), 439.62 [Mꢀ4I]4+ (calcd.
439.63).
3
3
NMR ([D6]acetone, 300 MHz): d = 7.77 (dd, JH,P = 11.6, JH,H = 8.2,
3
8H, PC6H4, Hortho), 7.38 (d, JH,H = 8.2, 8H, PC6H4, Hmeta), 7.08 (t,
3JH,H = 8.4, 4H, C6H4N), 6.40 (m, 12H, C6H4N), 3.63 (s, 8H, CH2O),

2152
I. Dorado et al. / Journal of Organometallic Chemistry 693 (2008) 2147–2152
[9] Poly(ethylene glycol)-terminated water-soluble carbosilane dendrimers have
4.10. Cross-coupling procedure
also been described B. Comanita, B. Noren, J. Roovers, Macromolecules 32
(1999) 1069–1072;
In a typical experiment, PhSi(OMe3) (0.20 mL, 1.07 mmol) was
introduced into a PTFE-valved ampoule and dissolved at room tem-
perature in 5 mL of a 0.5 M solution of NaOH in degassed water.
This solution was stirred for 10 min. 3-Bromopyridine (0.086 mL,
0.89 mmol) and the appropriate amount of palladium complex
(1.0 mol%; 11 mg for 5, 14 mg for 6, 15 mg for 7, and 20 mg for 8)
were then added and the mixture was stirred for 2 h at 140 °C.
The reaction mixture was allowed to cool to room temperature,
quenched with water, and extracted with diethyl ether (3 ꢂ 20 mL).
The combined organic layers were washed with brine (15 mL)
and dried over magnesium sulfate. The solution was filtered off
and the solvent removed in vacuo. Conversions were determined
by 1H NMR spectroscopy. For the recycling tests, the aqueous phase
was recovered, recharged with PhSi(OMe)3 (0.20 mL, 1.07 mmol)
and 3-bromopyridine (0.086 mL, 0.89 mmol), and the procedure
was repeated under the same conditions specified above.
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Acknowledgement
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We gratefully acknowledge financial support from the DGI-
´
Ministerio de Ciencia y Tecnologıa (Project CTQ2005-00795/BQU
and Ramón y Cajal contract to RA).
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